Number 301 (Story #4), December 31, 1996 by Phillip F. Schewe and Ben Stein SPACE WEATHER , like the more familiar lower-atmosphere weather, is a vast agglomeration of fronts and storms that changes by the minute. Filled with radiation and particles arriving from the sun and influenced by a potent terrestrial magnetic field, the near-earth space environment is increasingly important because of the numerous communications and positioning satellites parked there. Components on these craft, as well as astronauts and even passengers in high-flying aircraft, are also potentially endangered when storms on the sun send flurries of particles toward our planet. The National Space Weather Program, an inter-agency system of weather-forecasting instruments and data processing centers, will in coming years provide up-to-the-minute assessments of near-earth conditions. (Session at the American Geophysical Union meeting in San Francisco earlier this month.)